Research objectives are to evaluate the relationships that exist between visual pigments of vertebrates, those aspects of their behavior dependent on vision, and the photic environment. Specific studies will deal with the distribution of cone pigments in the retina of a representative group of vertebrates for which the spectral radiance of the backlight against which visual behaviors are performed is known. Using both microspectrophotometry and extraction spectrophotometry, both the types and amounts of each visual pigment will be ascertained. We presume that retinal architecture, with respect to types and amounts of different visual pigments, will relate to different lines of sight and the nature of the photic conditions associated with it. Since photic conditions along given lines of sight over the visual hemisphere vary in different habitats, the types and distributions of pigments should also relate to the differences in habitats. A more complete and exact comparative picture than now available of how the eye is adapted to accomplish a visual task should result. In addition, the study of environmentally induced changes in rhodopsin-prophyropsin ratios and, especially, total visual pigment in the eye will continue to be pursued. Attempts to detect and localize in specific tissues the "dehydrogenase" controlling retinal yields (reversibly) 3-dehydroretinal interconversions will be undertaken. If successful, knowledge of the enzyme should provide a clearer understanding of how light and/or thyroxine, for example, modifies retinal photosensitivity of a fish's or amphibian's eye.